1. Field of the Invention
This invention relates to a composite filament having excellent antistatic properties, and more particularly to a white, highly oriented, undrawn, conductive filament having excellent filament properties and antistatic properties which are durable when the clothing made thereof is worn.
More specifically, the present invention relates to a white, sheath-core composite filament having excellent antistatic properties, which comprises a sheath component of a fiber-forming polymer (A) and a core component of a thermoplastic polymer (B) containing a compound comprising a conductive material which comprises a metal oxide(s). The addition of an amount of only 0.01 to 10% by weight of this composite filament to a usual non-conductive fiber can provide the fabrics containing the fibers with excellent antistatic properties, which do not deteriorate even after being worn for one year.
2. Description of the Prior Art
Various conductive filaments have been proposed as having excellent antistatic properties. For example, there has been proposed a conductive filament comprising a conductive component which comprises a polymer containing a conductive carbon black mixed therein and a protective component which comprises a fiber-forming polymer.
However, such composite filaments utilizing a carbon black have a disadvantage, in that they are black or grey, and hence their use is limited.
Conductive filaments utilizing a white or colorless conductive metal oxide have recently been proposed to eliminate the above disadvantage. For example, Japanese Patent Application Laid-Open No. 6762/1982 and Japanese Patent Publication No. 29526/1987 propose a process of preparing a conductive composite filament comprising a mixture (conductive layer) of a conductive metal oxide and a thermoplastic resin and a fiber-forming thermoplastic polymer, said process comprising first preparing a composite filament as spun and drawing it and then further heat-treating the drawn filament to thereby restore the conductive layer. Where a thermoplastic resin is used as a binder for a conductive metal oxide, the obtained conductive layer is broken at the drawing process and as such the drawn filament cannot act as a conductive filament. Heat treatment is thus necessary when a thermoplastic resin, particularly a thermoplastic resin having high crystallinity, is used as the protective component for a conductive metal oxide. The process of the above patent, however, has a drawback of low productivity due to the presence of the heat treatment process after the heat drawing; and further the composite filament obtained by the process has a large drawback of insufficient durability when an article of clothing made thereof is actually worn. The "durability" of a composite filament herein is judged by whether or not the antistatic properties are still exhibited after a woven fabric comprising the conductive filament to be evaluated in an amount of 0.1 to 10% by weight has actually been worn for about 1 year. The standard for the upper limit of the static charge, specified in "Recommended Practice for Protection against Hazards Arising out of Electricity" in "Technical Recommendations" issued by Research Institute of Industrial safety of Labor Ministry, is 7 .mu. Coulomb/m.sup.2. This standard for the durability has not been met by conventional white or colorless conductive composite filaments. It has become clear from a study made by the present inventors that a thermoplastic polymer of, for example, polyethylene cannot give a conductive filament having a sufficient durability and that a fabric comprising such filament is hence not suited for use in work wears used for dangerous jobs. In the case where a crystalline thermoplastic resin is used as the thermoplastic polymer, the obtained conductive composite filament just after being produced has an electric resistance of less than 9.times.10.sup.10 .OMEGA./cm.multidot.filament which satisfies the static charge standard for fabrics. The filament, however, has a poor durability, and the fabric obtained therefrom hence has low antistatic properties and is difficult to put into practical use.
The present inventors have made a detailed study to obtain a conductive filament without the above-mentioned drawbacks, and, particularly, have intensively studied the relationship between the filament structure and the antistatic properties and the durability thereof, and found a composite filament having excellent antistatic properties and durability.